1. Field of the Invention
This invention relates to liquid processing method and apparatus for performing a coating process of processing liquid, such as resist liquid, to a substrate, for example, semiconductor wafer.
2. Background Art
In the manufacturing process for semiconductor devices or LCD substrates, a manufacturing technology called “photo lithography” is employed to form a desired resist pattern on the surface of a substrate. This technique is carried out during a series of processes of: coating resist liquid on a substrate, for example, semiconductor wafer that will be referred “wafer” hereinafter; exposing the resist liquid in accordance with a designated pattern; and developing the substrate after the exposure to form a desired pattern on the substrate.
The above coating process of the resist liquid is accomplished by first dropping the resist liquid onto the substantial center of a wafer supported by e.g. a spin chuck through application nozzles and secondly rotating the wafer to allow the resist liquid on the surface of the wafer to spread the same liquid from the center of the wafer to the periphery.
In the coating process, plural kinds of resist liquids may be used corresponding to the kinds of base films to be formed beneath the resist film, etching selectivities, thickness of the resist film and so on. In a constitution where coating nozzles are prepared for every resist liquids of different kinds and a common drive arm drives the coating nozzles between their standby positions and processing positions for applying the resist liquids, there are required many operative steps by the common drive arm grasping each of the application nozzles one after another and also troublesome tasks by the drive arm positioning the application nozzles to the wafer individually. From this point of view, the introduction of an “all-in-one” type coating nozzle unit having a plurality of nozzles built-in is recently contemplated, as shown with reference numeral 1 of FIG. 17 (see Japanese Patent Publication No. 3227642).
Meanwhile, since the resist liquid generally includes components of a resist film made of organic materials and a solvent for the components, such as thinner liquid, the resist liquid is easy to evaporate due to its contact with atmosphere. In order to prevent such evaporation of the resist liquid, therefore, there has been conventionally attempted a suck-back operation where the resist liquid is sucked into an application nozzle by e.g. approx. 2 mm after applying the resist liquid on a wafer, thereby establishing a condition where it is difficult for the resist liquid to contact with the atmosphere.
In spite of the above measure, however, the resist liquid has the tendency of evaporating with a passage of time. Therefore, if performing the coating process with the use of a coating nozzle where a predetermined interval has lapsed since the previous coating, then the resist liquid whose concentration has changed due to its dryness is applied, so that coating defectiveness is produced. Under such a situation, the coating process is practically carried out after throwing out the resist liquid dragged into the coating nozzles. Additionally, besides the above drainage before coating the resist liquid on a wafer, periodical drainage of the resist liquid in the nozzles has been performed in view of maintaining the quality of resist liquid in the nozzles.
We now discuss the coating process with the use of the above-mentioned all-in-one coating nozzle unit 1. Here, it should be noted that a single nozzle is activated and the other nozzles are not activated during the coating process. During the coating process, nevertheless, these nozzles not in use also move above a wafer W, together with the nozzle in use. Consequently, the resist liquid in the unused nozzles comes into contact with atmosphere, precipitating its dryness. Therefore, in the structure disclosed in the above publication No. 3227642, the coating nozzle unit 1 is covered with a cover body 11 and additionally, the cover body 11 is filled up with a thinner liquid 12 in view of preventing dryness of the resist liquid in the nozzle unit 1. In FIG. 17, reference numeral 13 denotes holes that are formed in the cover body 11 to discharge the resist liquid from the nozzles, corresponding to the nozzles respectively, and reference numeral 14 denotes a lid body for opening the holes 13 selectively.
However, it should be noted that the above-mentioned nozzle unit 1 is large-sized due to the installation of the cover body 11 outside the nozzles. If the number of nozzles built in the nozzle unit 1 increases, then it is large-sized furthermore. In spite of filling the interior of the cover body 11 with the thinner liquid 12, the actual coating process is carried out under conditions where the thinner liquid 12 is discharged from the cover body 11. Therefore, since the nozzles not in use are not blocked off from the atmosphere perfectly, the evaporation of the resist liquid in the nozzles is accelerated in consequence.
Thus, in case of the next coating process with the use of a different nozzle, the resist liquid in this nozzle has to be discharged in advance of the coating process. Additionally, as for a less frequently used nozzle, it is required to perform a periodical drainage of the resist liquid in such a nozzle frequently.
In this way, if it is carried out to drain the resist liquid from the nozzle with respect to each application of the coating liquid or periodically, then such an expensive resist liquid is wasted, so that an increased consumption of the resist liquid causes the manufacturing cost to be elevated. Under a situation, we and our inventors of the present invention are considering a method of reducing waste of the resist liquid without draining it with the adoption of a technique disclosed in Japanese Patent Publication (Kokai) No. 2003-178965. According to the technique, an air layer and a thinner layer are formed outside the resist liquid in the coating nozzle. That is, by suppressing contact of the resist liquid with atmosphere to prevent dryness of the resist liquid, its drainage before the coating process is prevented.
In the above publication No. 2003-178965, however, it is not supposed to apply this technique on an all-in-one type coating nozzle unit equipped with a plurality of nozzles. Additionally, there is neither description about a technique of forming the air layers and the thinner layers in a plurality of nozzles effectively nor description about a technique of first coating with the use of one nozzle and subsequently coating with the used of the other nozzle. Therefore, it should be noted that the concretization could not be attained by only the technique disclosed in the publication.